This invention relates to a moisture-permeable waterproof coated fabric. More particularly, it is concerned with a moisture-permeable waterproof fabric having an antimicrobial microporous polymeric coating thereon, the fabric having good moisture-permeability with durable waterproofness and antimicrobial properties that remain characteristic of the fabric even following multiple launderings. Procedures for making such fabrics are also described.
Coated fabrics suitable for use as rainwear function by blocking the pores of a woven, knitted or non-woven fabric with a cohesive polymer film which acts as a physical barrier against wind, water, and in the case of protective workwear, aggressive chemicals, oils, and greases. This barrier or coating distinguishes polymer coatings from chemical finishes which merely coat the individual fibers of a fabric without blocking the pores, and repel fluids by surface tension effects. Polymeric coatings have been based upon, initially rubber or synthetic or fluorocarbon rubbers, and more recently, polyurethanes, acrylics, silicone elastomers and polyvinylchlorides.
Fashion and leisurewear, particularly rainwear, require that the coated material is attractive with good drape and handle, be water repellent, although not necessarily for prolonged use in heavy rain, and that the fabric retain these properties after dry cleaning or laundering. There are several fabrics available that satisfy the conflicting requirements of waterproofness and breathability. One example is the laminated fabric known as Gore-Tex (W. L. Gore and Associates) which transmits perspiration through a microporous polytetrafluoroethylene (PTFE) film which is laminated between, usually, a woven nylon outer and a tricot inner fabric with a discontinuously applied adhesive. Another similarly qualified fabric, in the sense of waterproofness and breathability, is Entrant, which is a woven nylon fabric coated with a microporous polyurethane film formed by the so-called wet coagulation technique as in U.S. Pat. No. 4,429,000 to Toray Industries, Inc. Other polyurethane coated fabrics are described in U.S. Pat. No. 3,360,394 to Griffin. In the wet coagulation method a thin, microporous polyurethane layer is formed on a base fabric by applying a coating solution of a polyurethane dissolved in a polar organic solvent that will solubilize the polyurethane yet is miscible with water. The polymer solution is applied to the fabric substrate by knife coating or the like, then immersed in a bath of water which selectively dissolves or mixes with the organic solvent, exchanges water for the polar solvent and causes the previously dissolved polyurethane to coagulate leaving a thin, microporous coating having a cellular substructure on the fabric. Surface pores are generally one micron or less in diameter. Such pores are small enough to exclude water droplets and yet they provide a tortuous physical pathway from the base fabric to the coating surface, leading to a water-vapor-permeable fabric.
Rain-soaked and badly soiled garments must be cleaned or at least dried before long term storage to prevent proliferation of airborne bacteria and fungal spores that find a warm, moist environment hospitable. Such organisms find the cellular structure of this type of fabric attractive and can attack certain synthetic polymers, causing degradation of the polymer, in some cases, or at least permanent discoloration. Lomax, in the 1984 survey article Recent Developments in Coated Apparel, Journal of Coated Fabrics, Vol 14, October 1984, reports that natural rubber and some grades of PVC and polyurethane coatings have been protected by incorporated bacterocides and fungicides. In susceptible polymer coatings, biodegradation may be initiated in microscopic cracks and can eventually lead to delamination of the coating from the fabric and consequent loss of waterproofness.
The cellular structure of this type of microporous coating is subject to contamination with body oils, particularly when used as an article of apparel, due to direct contact with the skin or indirect transmission through a lining fabric. Thus, the potential exists for the production of undesirable odors, mildew and even discoloration since all the ingredients needed are present, namely, moisture, heat, and a nutrient for bacteria. It is also known that organic polymers are subject to bacterial attack which can result in deterioration of the polymer. A real need exists for the prevention of these undesirable occurrences.
The microporous coating of the present invention imparts to a microporous coated fabric the ability to prevent odor, discoloration, mildew, even discoloration due to bacterial growth. Furthermore, the coating retains its effectiveness even following repeated launderings.